I am trying to use the Google Flight RPC but am having trouble building a json array to post to it. The only documentation I've found is here. It describes what needs to be sent but doesn't explain how to construct the json array. Specifically, using PHP, I'm not sure how to build and post a json array using the following example from part 1 of the linked documentation.
[,[[,"fs","[,[,[\"SJC\"]\n,\"2012-04-05\",[\"EWR\",\"JFK\",\"LGA\"]\n,\"2012-04-12\"]\n]\n"]
]
,[,[[,"b_ca","54"]
,[,"f_ut","search;f=SJC;t=EWR,JFK,LGA;d=2012-04-05;r=2012-04-12"]
,[,"b_lr","11:36"]
,[,"b_lr","1:1528"]
,[,"b_lr","2:1827"]
,[,"b_qu","3"]
,[,"b_qc","1"]
]
]
]
The above does not appear to be properly formatted to be put into a json array. Additionally, HTTP request headers are needed. I assume these are set via cURL? I'm not clear on the documentation on how to do this.
I've tried several attempts and I don't get back any of the responses that are shown in the documentation.
Edit: Awesome, I got a Tumbleweed badge for this question! I would appreciate help. Thanks.
I was not able to find any documentation either.
However, if you go to https://www.google.com/flights/, open chrome console or firebug, click the network tab, then run a search, you will see that headers and body it makes for the RPC POST.
Sample Headers from the transfer:
Request URL:(I BROKE THE LINK) GOOGLE(dot)com /flights/rpc
Request Method:POST
Status Code:200 OK
Request Headers
:host:(I BROKE THE LINK) GOOGLE (dot) com
:method:POST
:path:/flights/rpc
:scheme:https
:version:HTTP/1.1
accept:/
accept-encoding:gzip,deflate,sdch
accept-language:en-US,en;q=0.8
content-length:169
content-type:application/json; charset=UTF-8
cookie:PREF=ID=f472fc4bbb95bc2b:U=9da5b7e4c1d04bda:FF=0:LD=en:TM=1390684154:LM=1390749713:GM=1:S=orUAMb3qaxBh99PJ; HSID=AHlw351sj7B7Om0t_; SSID=AKycPxLzyXkc4_tZJ; APISID=xKH5zAdc9vfBtiDy/Ab5TlD_Z4w2nP64Wl; SAPISID=7awo9qDssc3wr-fN/AQYOdvCN-I-UwtXQ1; NID=67=XnUn_DGdQDaeczlvXe-qTy9vy8gnQwhFwfRi52TRFS-_Dg-J58CgTGUY6Tkn3cCJYCcVJhK8unOrdffpgzeKed2jPqSazVI4Xplo5fW8-6wXoNi97L2gdoaOms0dKj4iOODoZpzd4DG_8YdQQcH6fl5xY__N929CJr8pdcAUwgnKf8X_mI8sLSB7CKVyS4ZvbGMCAiMLwIs1gJJz-UbppSj; S=travel-flights=5OJmMrbJoqLfOFzkZy285A; SID=DQAAAM0AAAAIGD56aXyxAxrRCSROmPy8AEtV3DaEwKT48aaZ98S35Nss09ishDZ3RxNT6ksikfAOJo-MLYVodF3jr-6imwzC8tRd7cxe-OoyafCZiGaf0qhp-yza4VZlAMInxGPhVae7wSXCRXlqb-wbYHBCHUSz_K5kYpvKwqC8pWuQ_6AUZa3WWqB6OmYpxuihxn3UxSve95zpkziyaDX0JFzUjyWX-0O_iIWZiEztywwyKVWCVv27ByGjIYTYV1G2byExt5M9-kEFpE_v0x8KgU7vleT
dnt:1
origin:(I BROKE THE LINK) SSL GOOGLE(dot)com
referer:(I BROKE THE LINK) SSL GOOGLE(dot)com flights
user-agent:Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/32.0.1700.107 Safari/537.36
x-gwt-cctoken:ADS25WMm8S7W0MlpX1-Lf_yNzQCrke7t6OvH2kFLkBJIH_Q-YTuu8VSHmgIxzFtGaL87SsM5PcZECRBP7IqMCbM5QKFVdWrw9hRIkHoL5oiyCzEu2ZCnKuhqvv2sUKcg4Z_HnajCZmM7aQ9nYsVMQnFxqrkgB2Cz7rAIP47zPJ_rakoyxlGE4yJvcuUeiQ
x-gwt-module-base:https://www.google.com/flights/static/
x-gwt-permutation:C8210E5F468630F84E578D8EDE10A1A0
Request Payload
[,[[,"no","[]","1531191655318648",11]],[,[[,"b_al","no:74"],[,"b_ahr","no:s"],[,"b_ca","103:34541"],[,"b_pe","4F2F79B9E3FB0.A40E22A.71A7"],[,"b_qu","0"],[,"b_qc","1"]]]]
Response Headersview source
alternate-protocol:443:quic
cache-control:no-cache, no-store, max-age=0, must-revalidate
content-encoding:gzip
content-length:75
content-type:application/json; charset=utf-8
date:Sat, 22 Feb 2014 05:00:17 GMT
expires:Fri, 01 Jan 1990 00:00:00 GMT
pragma:no-cache
server:GSE
status:200 OK
version:HTTP/1.1
x-content-type-options:nosniff
x-frame-options:SAMEORIGIN
x-xss-protection:1; mode=block
So, what you will likely have to do to get this to work correctly is to make a GET on the path /flights and read the headers, then put the headers in your POST request. (I have had to do similar things in the past). In order to figure out what fields are what I would play around with selecting different fields and seeing what changes in the JSON data that it posts.
Related
I did R&D on prevention of CRLF injection in php, but i didn't find any solution in mycase, as I'm using a burp suite tool to inject some headers using CRLF characters like the below.
// Using my tool i put CRLF characters at the start of my request url
GET /%0d%0a%20HackedHeader:By_Hacker controller/action
//This generates an header for me like below
HackedHeader:By_Hacker
So i can modify all headers by doing just like above
This tool is just like a proxy server so it catches the request and gives the response and we can modify the response in the way we want.
So i'm just modifying the response by injecting some headers using CRLF characters. Now the Server responds to this request by injecting the CRLF characters in the response.
I'm just worried as header fields like Pragma, Cache-Control, Last-Modified can lead to cache poisoning attacks.
header and setcookie contain mitigations against response/header splitting, But these can't support me in fixing the above issue
Edit
When i request to mysite.com contact us page like below This is the request I captured in my tool like below
Request headers:
GET /contactus HTTP/1.1
Host: mysite.com
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Connection: keep-alive
And i get the Response HTML for the above request
Now for the same request using the tool i'm adding custom headers just like below
Request Headers:
GET /%0d%0a%20Hacked_header:By_Hacker/contactus HTTP/1.1
Host: mysite.com
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Connection: keep-alive
Response Headers:
HTTP/1.1 302 Found
Date: Fri, 10 Jul 2015 11:51:22 GMT
Server: Apache/2.2.22 (Ubuntu)
Last-Modified: Fri, 10 Jul 2015 11:51:22 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Location: mysite.com
Hacked_header:By_Hacker/..
Vary: Accept-Encoding
Content-Length: 2
Keep-Alive: timeout=5, max=120
Connection: Keep-Alive
Content-Type: text/html; charset=UTF-8
You can see the injected header Hacked_header:By_Hacker/.. in the above response
Is there anyway in php or apache server configuration to prevent such kind of headers' hack?
Not sure why all the down votes - infact, it is an interesting question :)
I can see that you have tagged CakePHP - which means your app is using Cake Framework... Excellent! If you are using Cake 3 , it is automatically strip off : %0d%0a
Alternatively, where you receive the response header, just strip off %0d%0a and you are good!
Where things like these could be applied - a 3rd party API response or say.... a Webhook response! or a badly sanitized way to handle intl.. example : lang=en to lang=fr where the GET param is directly set as response header... That would not be a wise move!
Ideally, the responses will be as GET and not in the header but either way just strip the %0d%0a and you are good.
Answering your edit.
You can see the injected header Hacked_header:By_Hacker/.. in the above response
That injected header cannot be controlled or stopped, mate. We do not have control over what the other server does.
The question is.. What do you do with the response header?
The answer is... You sanitize it, as ndm said you need to sanitize the input.. What you get as a response IS an input. As soon as you detect %0d%0a, discard the response.
Need code work?
<?php
$cr = '/\%0d/';
$lf = '/\%0a/';
$response = // whatever your response is generated in;
$cr_check = preg_match($cr , $response);
$lf_check = preg_match($lf , $response);
if (($cr_check > 0) || ($lf_check > 0)){
throw new \Exception('CRLF detected');
}
locally and on the server, I get different results with the same code.
Locally my results arrive as string, while on the server, the same code returns JSON object. Can anybody tell me why?
The javascript:
$.post(
url, // Various urls of type '/users/add_secondary_email_ajax'
data,
function(res){
if (typeof(res.success)=='undefined'){
ModalManager.update_body_html(res);
}else{
callback_success(res);
}
}
);
The CakePHP:
$this->autoRender = false;
$this->RequestHandler->respondAs('json');
echo json_encode( array('success'=>true) ); // this arrives as string locally
return;
I also had this working on my other computer, but not this one. Could it be some PHP settings?
Both computers have the same versions of Browser & CakePHP version (2.2.3).
I see differences in PHP and Apache versions. Could be settings also, but I don't know where to look.
Header On Broken Computer:
Request URL:localhost/alert_subscribers/subscribe_ajax
Request Method:POST
Status Code:200 OK
Request Headers
Accept:*/*
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-US,en;q=0.8,bg;q=0.6
Connection:keep-alive
Content-Length:153
Content-Type:application/x-www-form-urlencoded; charset=UTF-8
Cookie:timezoneoffset=-120; viewedJobsGuest=[24]; __atuvc=13%7C11%2C46%7C12; CAKEPHP=dfbf9407743d43eb619a42aa5dbda735; toolbarDisplay=hide
Host:jobsadvent.dev
Origin:URL:localhost
Referer:URL:localhost/search
User-Agent:Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.152 Safari/537.36
X-Requested-With:XMLHttpRequest
Form Data
data[title]:the title
data[email]:fake2#hotmail.com
data[alert]:1
Response Headers
Connection:Keep-Alive
Content-Length:57
Content-Type:text/html
Date:Fri, 21 Mar 2014 10:19:06 GMT
Keep-Alive:timeout=5, max=100
Server:Apache/2.2.26 (Unix) DAV/2 PHP/5.4.24 mod_ssl/2.2.26 OpenSSL/0.9.8y
X-Powered-By:PHP/5.4.24
Header on Working computer
Request URL:http://domain.com/alert_subscribers/subscribe_ajax
Request Method:POST
Status Code:200 OK
Request Headers
Accept:*/*
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-US,en;q=0.8,bg;q=0.6
Connection:keep-alive
Content-Length:162
Content-Type:application/x-www-form-urlencoded; charset=UTF-8
Cookie:__atuvc=1%7C10%2C5%7C11; timezoneoffset=-120; CAKEPHP=sb3013ffk40h7o1jhsl8ulqfj4; toolbarDisplay=hide
Host:domain.com
Origin:http://domain.com
Referer:http://domain.com/search
User-Agent:Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.152 Safari/537.36
X-Requested-With:XMLHttpRequest
Form Data
data[title]:the title
data[email]:fake#hotmail.com
data[alert]:1
Response Headers
Connection:close
Content-Length:57
Content-Type:application/json
Date:Fri, 21 Mar 2014 10:24:32 GMT
Server:Apache/2.2.15 (CentOS)
X-Powered-By:PHP/5.3.3
As for the routes.php file both are identical and contain the following line:
Router::parseExtensions('json');
This could be an issue with your apache settings:
The answer given on Apache sending incorrect response header for .js files suggests that you need something like
<FilesMatch \.php$>
SetHandler application/x-httpd-php
</FilesMatch>
to get the right content types.
Refer to the jQuery.post() documentation. There is a fourth parameter (dataType) that you can use that will force jQuery to coerce the response to the correct datatype. You will need to set that equal to 'json' if you want an object back.
Well, no - computer 1 it is application/json and in the other it is text/html. Both have the same code I posted up there.
There's your problem. jQuery uses the response's Content-Type header as a guide.
The CakePHP docs seem to indicate that $this->RequestHandler->respondAs() may work better if you pass it application/json rather than just json.
JSON parsing should fix it.
$.post(
url, // Various urls of type '/users/add_secondary_email_ajax'
data,
function(res){
var result = JSON.parse(res);
if (typeof(result.success)=='undefined'){
ModalManager.update_body_html(res);
}else{
callback_success(res);
}
}
);
I would set the contentType and dataType in your $.POST request.
$.POST({
contentType : "application/x-www-form-urlencoded; charset=UTF-8",
dataType : "json"
})
when calling api:
$.post();
"dataType" param should be set as "json".if it is not sepecfied, ajax will intelligent guessed (xml, json, script, text, html...).see manual here:
so how could the ajax guess the type of data ?
There is a response header, "Content-Type:", by which the server tell the client what type is data. I think , ajax need this header to guess the data type.
this is your broken computer's response:
Content-Type:text/html
and this is your working computer's response:
Content-Type:application/json
if you don't want to specified the param "dataType" of $.post(), you can change the response header, there must be many ways to change it, like this:
<?php
header("Content-Type:application/json");
?>
That could be messy, but don't get worried until there's something to really worry about.
Statement of fact: one of your servers is behaving as expected and the other is not.
With the way that your error is manifesting, it sounds an awfully lot like you are not specifying your request specifically enough or your borked server is failing Content Negotiation.
There are two basic things that come into play here that you likely already know about: the requester's "Accept" header that allows the user agent to specify the content types that it is willing to receive and the server's ability to interpret that request and serve it appropriately. In absence of an explicitly set Accept header, text\html is the default response type.
Accept Header: RFC2616 Hypertext Transfer Protocol Section 14.1
The Accept request-header field can be used to specify certain media
types which are acceptable for the response. Accept headers can be
used to indicate that the request is specifically limited to a small
set of desired types, as in the case of a request for an in-line
image.
The asterisk "" character is used to group media types into ranges,
with "/" indicating all media types and "type/" indicating all
subtypes of that type. The media-range MAY include media type
parameters that are applicable to that range.
The accept headers that you set for each request indicate that you don't care what the server gives you. You might try setting your accept header to application/json and see if the "broken" server can interpret it and serve you. If that works, then it seems you're just running into an inconsistency with the way the servers are defaulting their response types. This even looks to be what you're asking for it to do. You said you accept all response types. If you don't specify something specific, the most reasonable type for a server to give you is text/html
MIME Types: RFC 2046 Multipurpose Internet Mail Extensions
JSON: RFC 4627 The application/json Media Type for JavaScript Object Notation (JSON)
If setting the Accept header doesn't work for you, you're going to want to check your server's MIME type registration to make sure that [application\json] is registered and configured. That is not an esoteric configuration subject, so it should be available in any server's configuration documentation.
If neither of those approaches work, then the solution is to unplug the offending machine, carry it to the top of the building, and throw it as far as you can.
I am using the CakePHP Cart Plugin to add shop functionality to a website. I want to add items to the shopping cart using an AJAXified button. Submitting the form works fine. I am having trouble to correctly return just the shopped item as JSON data in method captureBuy() on line 210.
Which settings do I need to use and where/how do I set them? Any hint appreciated!
This is the request which is being sent:
Request URL:http://shop.site/carts_items/buy
Request Method:POST
Status Code:302 Found
Request Headers
Accept:application/json, text/javascript, */*; q=0.01
Accept-Encoding:gzip,deflate,sdch
Accept-Language:de-DE,de;q=0.8,en-US;q=0.6,en;q=0.4
Connection:keep-alive
Content-Length:134
Content-Type:application/x-www-form-urlencoded; charset=UTF-8
Cookie:CAKEPHP=cd4611d0bf0100247928990a8efa72d0; rememberMe[User]=2....BmKdEs;
DNT:1
Host:shop.site
Origin:http://shop.site
Referer:http://shop.site/offer/1
User-Agent:Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/30.0.1553.0 Safari/537.36 SUSE/30.0.1553.0
X-Requested-With:XMLHttpRequest
Form Data
_method:POST
data[CartsItem][foreign_key]:72
data[CartsItem][model]:Product
data[CartsItem][quantity]:1
Response Headers
Connection:keep-alive
Content-Type:text/html; charset=UTF-8
Date:Mon, 23 Sep 2013 20:32:28 GMT
Location:http://shop.site/offer/1
Server:nginx/1.0.15
Transfer-Encoding:chunked
Define "not correctly". Paste your request and response from your network tab (in Chrome).
You don't have to set the items, the CartManager is already setting them to the view and serializes them. At least it should.
Make sure you have the RequestHandler component loaded as well.
I'm trying to get this CrunchBase API page as a string in PHP. When I visit that page in a browser, I get the full response (some 230K characters); however, when I try to get the page in a script, the response is much shorter (24341 characters on a server and 36629 characters locally, with exactly the same number of characters for other long CrunchBase pages). To get the page, I am using a function almost identical to drupal_http_request() although I'm not using Drupal. (I have also tried using cURL and file_get_contents() and got the same result. And now that I'm thinking about it I have experienced the same from CrunchBase in Python in the past.)
What could be causing this and how can I fix it? PHP 5.3.2, Apache 2.2.14, Ubuntu 10.04. Here are additional details on the response:
[protocol] => HTTP/1.1
[headers] => Array
(
[content-type] => text/javascript; charset=utf-8
[connection] => close
[status] => 200 OK
[x-powered-by] =>
[etag] => "d809fc56a529054e613cd13e48d75931"
[x-runtime] => 0.00453
[content-length] => 230310
[cache-control] => private, max-age=0, must-revalidate
[server] => nginx/1.0.10 + Phusion Passenger 3.0.11 (mod_rails/mod_rack)
)
I don't think it's a user agent issue as I used User-Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/536.5 (KHTML, like Gecko) Chrome/20.0.1092.0 Safari/536.6 in the request.
UPDATE
According to this thread I needed to add the Accept-Encoding: gzip, deflate header to the request. That does result in a longer request result, but now I have to figure out how to inflate it. The gzinflate() function fails with a Warning: Data error. Any thoughts on how to inflate the response?
See the comments in the PHP docs about gzinflate(), specifically the remarks about stripping the initial bytes. The last comment did the trick for me:
<?php $dec = gzinflate(substr($enc,10)); ?>
Though it seems that the number of bytes to be stripped depends on the original encoder. Another comment has a more thorough solution, and a reference to RFC1952 for further reading.
Evidently gzdecode() is meant to address to this issue, but it hasn't been released yet.
ps -- I deleted my comment about the returned data being plain text. I was wrong.
I'm been stuck on this problem for a while and I'm pretty sure it must be something quite simple that hopefully someone out there can shed some light on.
So, I'm currently using jQuery UI's Autocomplete plugin to reference and external PHP which gets information from a database (in an array) and sends it to a JSON output.
From my PHP file (search.php) when I do this:
echo json_encode($items);
My output (when looking at the search.php file) is this:
["Example 1","Example 2","Example 3","Example 4","Example 5"]
Which is valid JSON according to jsonlint.com
The problem is that when I use jQuery UI's Autocomplete script to reference the external search.php file, Chrome just gives me the following error:
GET http://www.example.com/search.php?term=my+search+term 404 (Not Found)
I have tried inputting the JSON code straight into the 'Source:' declaration in my jQuery, and this works fine, but it will not read the JSON from the external PHP file.
Please can someone help?
Here's my code:
HMTL
<p class="my-input">
<label for="input">Enter your input</label>
<textarea id="input" name="input"
class="validate[required]"
placeholder="Enter your input here.">
</textarea>
</p>
jQuery
$(function() {
$( "#input" ).autocomplete({
source: "http://www.example.com/search.php",
minLength: 2
});
});
PHP
header("Content-type: application/json");
// no term passed - just exit early with no response
if (empty($_GET['term'])) exit ;
$q = strtolower($_GET["term"]);
// remove slashes if they were magically added
if (get_magic_quotes_gpc()) $q = stripslashes($q);
include '../../../my-include.php';
global $globalvariable;
$items = array();
// Get info from WordPress Database and put into array
$items = $wpdb->get_col("SELECT column FROM $wpdb->comments WHERE comment_approved = '1' ORDER BY column ASC");
// echo out the items array in JSON format to be read by my jQuery Autocomplete plugin
echo json_encode($items);
Result
In browser, when information is typed into #input
GET http://www.example.com/search.php?term=Example+1 404 (Not Found)
Update: the real PHP url is here: http://www.qwota.co.uk/wp/wp-content/themes/qwota/list-comments.php?term=Your
Please help!
UPDATE: ANSWER
The answer to my problem has been pointed out by Majid Fouladpour
The problem wasn't with my code but rather with trying to use WordPress' $wpdb global variable as (as far as I understand) it includes it's own headers, and anything outside of it's usual layout will result in a 404 error, even if the file is actually there.
I'm currently trying to get around the problem by creating my own MySQL requests and not using WordPress's global variables / headers.
PS. Majid, I'll come back and give you a 'helpful tick' once StackOverflow lets me! (I'm still a n00b.)
Are you sure the path source: "http://www.example.com/search.php" is correct?
You have to make sure that the target URL exists. If you are really using http://www.example.com/search.php then, wk, it simply does not exist, so this is why it does not work.
Update
Since you have a real URL that's working (I tested it!), here are a few steps you can take:
Make sure there's no typo. If there's one, fix it.
Make sure you can open that URL from your browser. If you cannot, then you might be having network access problems (firewall, proxy, server permission issues, etc.)
Try redirecting to another know URL, just to make sure. The 404 error is really a "not found" error. It cannot be anything else.
I think the include is the issue. As Majid pointed out... use the below include instead.
include("../../../wp-load.php");
Good luck!
Your apache server is sending wrong headers. Here is a pair of request and response:
Request
GET /wp/wp-content/themes/qwota/list-comments.php?term=this HTTP/1.1
Host: www.qwota.co.uk
User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:2.0.1) Gecko/20100101 Firefox/4.0.1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip, deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 115
Connection: keep-alive
Cookie: __utma=142729525.1341149814.1305551961.1305551961.1305551961.1; __utmb=142729525.3.10.1305551961; __utmc=142729525; __utmz=142729525.1305551961.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none)
Response headers
HTTP/1.1 404 Not Found
Date: Mon, 16 May 2011 13:28:31 GMT
Server: Apache
X-Powered-By: PHP/5.2.14
X-Pingback: http://www.qwota.co.uk/wp/xmlrpc.php
Expires: Wed, 11 Jan 1984 05:00:00 GMT
Cache-Control: no-cache, must-revalidate, max-age=0
Pragma: no-cache
Last-Modified: Mon, 16 May 2011 13:28:31 GMT
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Transfer-Encoding: chunked
Content-Type: text/html; charset=UTF-8
Response body
["Bake 'em away... toys.","Content precedes design. Design in the absence of content is not design, it\u2019s decoration.","Hanging on in quiet desperation is the English way.","I'm a reasonable man, get off my case.","Look at me, Damien! It's all for you!","Never get out of the boat... absolutely god damn right.","That gum you like is going to come back in style.","The secret to creativity is knowing how to hide your sources.","Things could be different... but they're not.","Your eyes... they turn me."]
So, even though you receive back response from the server, it has HTTP/1.1 404 Not Found in the headers. Someone may be able to investigate this and provide a potential reason and solution.